Don't validate RDAP nameserver names using validateDomainName

The nameserver may be external, in which case its TLD will not appear in our
list of valid TLDs, and the search will be rejected erroneously.

Tests for letter case canonicalizations also added at reviewer's suggestion.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171985702

java/google/registry/flows/host/HostFlowUtils.java

@@ -39,7 +39,7 @@ import org.joda.time.DateTime;
 public class HostFlowUtils {
 
   /** Checks that a host name is valid. */
-  static InternetDomainName validateHostName(String name) throws EppException {
+  public static InternetDomainName validateHostName(String name) throws EppException {
     checkArgumentNotNull(name, "Must specify host name to validate");
     if (name.length() > 253) {
       throw new HostNameTooLongException();